Intro: Replacing a Membrane Keypad With Microswitches
This is a rough outline of what you'll need to do to replace a keypad from a microwave, washing machine ,etc. with microswitches. It will offer enhanced durability and some savings.
The standard disclaimer applies- I'm not responsible if you kill\maim yourself, break your appliance, or set the cat on fire. If you don't think you're up to it, you're probably not.
I came up with the idea to replace the keypad for our microwave with microswitches 'cause-
1> It was out of warranty
2> Samsung charges Rs.800 for the membrance only, installation extra. For a fact, a membrane keypad usually costs around Rs.350. Plus I've been a little annoyed with Samsung since my phone died one month out of warranty.
3> Microswitches are more durable than membranes.
4> I wanted an excuse to crack open the oven and use my new hot glue gun. :D
This is only a rough guide- your appliance will be a little different and the steps may slightly change as well. I'm sure there are better ways to do some of the things, even I would do it differently if I were to do it again. I will not be detailing how to open a bolt or how to solder. or use a glue gun (I think I need to learn it :) ).
Step 1: Detach the Keypad Panel
Open the oven cover, and get to the main controller board. It's the one with the display and keypad attached. Separate the keypad panel from the board. It should look somewhat like this when you're done.
Step 2: The Matrix!
Peel the top layer of the graphic. A thin knife does it nicely. Underneath it, you'll find the matrix with the pads for buttons.
Step 3: Mapping the Matrix
You'll need to write out which trace on the connector goes to which button- this step can be done both visually as well as with a multimeter. The multimeter must be set to resistance mode, as the continuity mode does not ring for larger values of resistance. The number of connections is exactly double of the number of buttons. Some traces connect to other traces instead of new buttons- 6 & 7 in this case are connected to 9 and 10. I suspect this is for some kind of check-keypad-present thing, so I shorted out those traces on the controller board. It is essential not to make a mistake in mapping out the matrix.
Step 4: Fixing the Buttons
Drill using the matrix as a guide, and then peel off the matrix. Glue in new buttons. This was the first time I used hot glue, and I was quite sloppy. Using a guide for proper button height helps.
Step 5: Solder the Buttons
Solder the buttons. There was a lot of space, so I did a nice and sloppy job here. Using a different colour for each trace helps a lot. The connector is optional- you can solder directly to the main board if needed. I used a zip tie to secure the bunch of wires.
Step 6: Finishing Up
Glue the old label on the buttons. I used glue only on the edges. I also hot glued a connector on the main board to enable easy removal, but it is optional. Fit everything back together and test it!